Fuel cells utilize the chemical conversion of a fuel with oxygen to water, in order to generate electrical energy. For this purpose, fuel cells contain the so-called membrane electrode unit (MEA for membrane electrode assembly) as the core component, which is a composite of an ion-conducting, in particular, proton-conducting membrane and an electrode (anode and cathode) situated on each side of the membrane. During operation of the fuel cell, the fuel, in particular, hydrogen H2 or a hydrogen-containing gas mixture, is fed to the anode, where an electrochemical oxidation and simultaneous discharge of electrons takes place (H2→2 H++2 e−). A (water-bound or water-free) transport of the protons H+ takes place from the anode chamber into the cathode chamber via the membrane, which separates the reaction chambers from one another in a gas-tight manner and electrically isolates them. The electrons e− provided at the anode are fed to the cathode via an electric line. The cathode is supplied with oxygen or an oxygen-containing gas mixture, causing a reduction in oxygen and absorption of electrons to take place (½O2+2 e−→O2−). At the same time, these oxygen anions react in the cathode chamber with the protons transported via the membrane while forming water (2H++O2−→H2O).
The fuel cell is generally formed by a plurality of membrane electrode units assembled in a stack, the electrical outputs of which are cumulative. A bipolar plate assembly (also referred to as bipolar plate), which is used to supply process gases to the anode or cathode of the adjacent membrane electrode units, is situated between two membrane electrode units (MEA) in each fuel cell stack. The assembly is also used to dissipate heat. In addition, bipolar plates are made of an electrically conductive material in order to be able to establish an electrical connection. Thus, they exhibit the three-fold function of supplying process gas to the membrane electrode units, their cooling and electrical connection. Bipolar plates are frequently constructed of two profiled bipolar plate halves, a so-called anode plate and a cathode plate, between which a coolant channel is formed.
Bipolar plates and fuel cell stacks of compact structures are known in the prior art.
DE 11 2005 003 103 B4 describes a fuel cell stack having bipolar plates, which include two nested half plates in certain areas. A solution for a transition between an area having a nested configuration to a non-nested area is described. The transition in this case lies between an active and an inactive area of the fuel cell stack.
The bipolar plate shown in DE 10 2013 208 450 A1 solves the problem of reducing the overall height while simultaneously maintaining a power density. For this purpose, the design of the bipolar plate includes two sheet metal layers. Each of the two sheet metal layers has in cross section a periodic structure with elevations and recesses of the same periodic length. The two sheet metal layers are inserted into each other so that cooling channels are formed between the elevations and recesses of the sheet metal layers.
The two half plates of known bipolar plates are normally of equal thickness.